Dual-alloy Method Research Articles

Improvement of thermal stability by co-introducing Dy and Co with dual-alloy method in NdFeB magnets

A dual-main-phase magnet with excellent thermal stability was prepared by co-mixing two types of magnetic powders, which was the conventional N55-grade powder without Dy elements, while the Co and Dy contents reached 50 wt% and 6 wt% respectively in another Co-rich powder. Studies showed that the magnetic properties along with the thermal stabilities of the magnets exhibited significant differences with the changes in the mixing ratio of the two powders. Especially, when mixing the two powders in equal proportions, a great remanence temperature coefficient of −0.0725 %/°C at 20–100 °C was obtained with a rather high Curie temperature of 581 °C, possessing its magnetic properties with Br = 12.58 kGs, Hcj = 15.9 kOe, and (BH)max = 36.88 MGOe. Note that as the proportion of Co-rich powder increased to 2/3, although the Curie temperature of the prepared magnets further increased to 622 °C, both the remanence temperature coefficient and the magnetic properties deteriorated significantly. The phase composition and microstructure analyses revealed that when the proportion of added Co-rich component exceeded 1/2, the RE(Fe,Co)2B phase transformed into the RE(Fe,Co)4B phase, and a significant amount of RE(Fe,Co)1.8B0.2 phase precipitated at the grain boundaries, leading to a deterioration in magnetic performance. In addition, dynamic domain evolution analyses under variable temperature conditions demonstrated the positive effect of the appropriate introduction of Co/Dy on the anti-demagnetization in high temperatures. This work provides insights and an experimental foundation for the development of high-performance magnets with high thermal stability, used in high-temperature environments.

Analysis on coercivity enhancement mechanism of grain-boundary-diffused and Dual-alloyed Nd-Fe-B Magnets

With the rapid development of application fields, such as the green energy industry, has resulted in increased demand for magnetic characteristics, especially the coercivity (Hcj). In this paper, two types of (Nd, Dy)-Fe-B magnets with comparable Hcj values were prepared using by grain boundary diffusion (GBD) method and dual alloy (DA) method. The composition, microstructure, domain structure, and magnetization reversal process of GBD and DA magnets were subjected to comparison. Additionally, an analysis of the specific coercivity mechanism was also conducted by fitting the Brown's equation. The results of composition and microstructure analysis revealed the formation of core-shell structural grains were formed in both GBD and DA methods. Specifically, the GBD method exhibited a higher concentration of Dy in the shell, constituting 26.8 % of the total rare earth (RE) content. In contrast the DA magnets had Dy accounting for 15.8 % of the total RE content in the shell. This discrepancy was identified as the primary factor contributing to the superior efficiency in enhancing the coercivity (Hcj) observed in the GBD method. The fitting results showed that GBD magnets were more inclined to nucleate in the core region in grain, whereas DA magnets nucleate at the edge of the grain shell layer. Both the observation of magnetic domains and magnetization reversal processes analysis revealed that the demagnetization process in GBD magnets is more uniform, which leads to better squareness. Our finding can provide theoretical and experimental basis for the preparation of high-performance Nd-Fe-B magnets.

Optimization of grain boundary by Mo nano-powder to enhance the coercivity of NdFeB magnets

The Mo doped NdFeB magnets were prepared by the dual alloy method. Through transmission electron microscopy (TEM) and electron probe microanalyzer (EPMA), it is observed that the Mo element is mostly distributed at the grain boundary, which isolates the main phase grains, thus improving the intrinsic coercivity (Hcj) of the magnets. When the addition of Mo nano-powder is increased from 0 to1.0 wt%, the Hcj of the magnet is significantly improved. Especially, when the addition of Mo nano-powder is 0.8 wt%, the Hcj of the magnet is 138 kA/m higher than that of the magnet without Mo addition. The current research work shows that the Mo doped magnet prepared by the dual alloy method effectively improves the Hcj of NdFeB magnets, which has practical application value and theoretical significance for the research and development of high-performance NdFeB magnets.

Temperature dependence of magnetization reversal mechanism in misch-metal substituted Nd-Fe-B magnets sintered by dual alloy method

The substitution of Nd by misch-metal (MM) in Nd-Fe-B permanent magnets has attracted extensive attention due to the effective reduction of production cost and rational utilization of rare earth resources. In particular, multi-main phase (MMP) magnets prepared by dual alloy method possess a higher permanent magnetic performance than that of single main phase (SMP) magnets. However, the coercivity mechanism of MMP magnets is different from the nucleation and propagation of SMP magnets, especially the interactions of different 2:14:1 main phases have not been clarified. In this study, we investigated the temperature dependence of magnetization reversal mechanism in (MM,Nd)-Fe-B magnets by using recoil loops, minor hysteresis loops, first-order and second-order reversal curves. It found that with the increase of temperature, the magnetic moments motion is mainly affected by long-range magnetostatic interaction rather than exchange coupling. The weakened coupling interaction makes the demagnetization process of softer and harder magnetic phases asynchronous. The thermal activation energy barrier index related to coercivity mechanism is 1.45, 1.18 and 1.0 at 200 K, 300 K and 380 K, respectively. It indicates that nucleation and expansion of reversed domains are the main mechanisms controlling the magnetization reversal process at low temperature. While the coercivity at high temperature is mainly determined by the domain wall pinning mechanism. In addition, we noted that both two coercivity mechanisms coexist in MMP magnets at 300 K. Micromagnetism has also been used to verify the coercivity mechanism of (MM,Nd)-Fe-B magnets sintered by dual alloy method, which is of great significance for improving the magnetic properties of high abundance rare earth magnets.

Magnetic properties and rare earth element diffusion behavior of hot-deformed nanocrystalline dual-main-phase Nd-Ce-Fe-B magnets.

To inhibit the magnetic dilution effect of Ce in Nd-Ce-Fe-B magnets, a dual-alloy method is employed to prepare hot-deformed dual-main-phase (DMP) magnets using mixed nanocrystalline Nd-Fe-B and Ce-Fe-B powders. A REFe2 (1 : 2, where RE is a rare earth element) phase can only be detected when the Ce-Fe-B content exceeds 30 wt%. The lattice parameters of the RE2Fe14B (2 : 14 : 1) phase exhibit non-linear variation with the increasing Ce-Fe-B content due to the mixed valence states of Ce ions. Owning to inferior intrinsic properties of Ce2Fe14B compared to Nd2Fe14B, the magnetic properties of DMP Nd-Ce-Fe-B magnets almost decrease with the increase of Ce-Fe-B addition, but interestingly, the magnet with 10 wt% Ce-Fe-B addition exhibits an abnormally increased intrinsic coercivity H cj of 1215 kA m-1, together with the higher temperature coefficients of remanence (α = -0.110%/K) and coercivity (β = -0.544%/K) in the temperature range of 300-400 K than the single-main-phase (SMP) Nd-Fe-B magnet with H cj = 1158 kA m-1, α = -0.117%/K and β = -0.570%/K. The reason may be partly attributed to the increase of Ce3+ ions. Different from the Nd-Fe-B powders, the Ce-Fe-B powders in the magnet are difficult to deform into a platelet-like shape because of the lack of low melting point RE-rich phase due to the precipitation of the 1 : 2 phase. The inter-diffusion behavior between the Nd-rich region and Ce-rich region in the DMP magnets has been investigated by microstructure analysis. The significant diffusion of Nd and Ce into Ce-rich and Nd-rich grain boundary phases, respectively, was demonstrated. At the same time, Ce prefers to stay in the surface layer of Nd-based 2 : 14 : 1 grains, but less Nd diffuses into Ce-based 2 : 14 : 1 grains due to the 1 : 2 phase presented in the Ce-rich region. The modification of the Ce-rich grain boundary phase by Nd diffusion and the distribution of Nd in the Ce-rich 2 : 14 : 1 phase are beneficial for magnetic properties.

Preparation of hot worked dual-main phase Nd-Ce-Fe-B magnets and properties modification by grain boundary diffusion

Hot pressed and hot deformed nanocrystalline Nd-Ce-Fe-B magnets were prepared by dual-alloy method using melt-spun Nd-Fe-B and Ce-Fe-B powders with various weight ratios. For both hot pressed and hot deformed magnets, increasing Ce-Fe-B addition reduces the magnetic properties, but 10 wt. % Ce-Fe-B leads to an abnormal increase of coercivity. As a result, the remanence Jr = 1.21 T, intrinsic coercivity Hcj = 1215 kA/m, and maximum energy product (BH)max = 266 kJ/m3 are obtained for the magnets with 10 wt. % Ce-Fe-B. To modify their properties, the dual-main phase magnets are treated by grain boundary diffusion of Nd50Tb20Cu30 alloy. The coercivity of the deformed magnet with 10 wt. % Ce-Fe-B addition increased from 1215 kA/m to 1402 kA/m after diffusion, which is comparable to that of the as-diffused Nd-Fe-B magnets (1495 kA/m). For the magnet with 30 wt. % Ce-Fe-B addition, a 50% increase of coercivity, about 376 kA/m, was obtained by diffusion. The microstructure characterizations demonstrated that the modification of grain boundary phase by the elimination of RE5Fe17 phase and the formation more significant core-shell structure of the Nd-rich hard magnetic 2:14:1 phase by Tb diffusion are responsible for the improved coercivity.

Extraordinary simultaneous enhancement of the coercivity and remanence of dual alloy HRE‐free Nd‐Fe‐B sintered magnets by post‐sinter annealing

• Both the remanence and coercivity are improved after the 2nd annealing process. • The coercivity is hugely increased from 10.09 kOe for the as-sintered sample to 17.19 kOe for the 2nd annealed magnet, with a significant increment of 70.37%. • The matrix grains are enveloped by a (Pr,Nd,Cu,Ga)-enriched layer after the 2nd annealing process. • HRE-free Nd-Fe-B sintered magnets with excellent comprehensive magnetic properties were manufactured by Pr-Fe-Ga boundary addition. Post-sinter annealing process plays an important role in the microstructures and magnetic properties of the Nd-Fe-B sintered magnets. In this paper, systematically investigated are the magnetic properties and microstructures of the as-sintered and post-sinter annealed Nd-Fe-B magnets with Pr-Fe-Ga boundary addition. Two choice consecutive annealing methods are adopted at high and low temperatures, namely the 1 st annealing at 880 ºC for 2 h and then the 2 nd annealing at 440 ºC for 3 h. It is exceptional to find out that both the remanence and coercivity are improved after 2 nd annealing process for this type of magnet. The coercivity is hugely increased from 10.09 kOe for the as-sintered sample to 17.19 kOe for the 2 nd annealed magnet, with a significant increment of 70.37% in coercivity. The extraordinary magnetic properties of B r =14.44 kGs, H cj =17.19 kOe and ( BH ) max =51.08 MGOe are obtained for the designated Nd-Fe-B sintered magnets without heavy rare earth (HRE) elements manufactured by dual alloy method. The Curie temperature is monotonically decreased from 634 K to 602 K while the c -axis alignment degree is optimized after annealing. Microstructural observation and analysis indicate that the elemental distribution patterns are altered after the 2 nd annealing. The diffusion of the aggregate (Pr,Nd,Cu,Ga)-rich phase from triple junctions into the grain boundary regions is ascribed to the formation of thin and continuous grain boundary layer, which is critical to improve the microstructures and magnetic properties.

Exchange interaction and demagnetization process of high-abundance rare-earth magnets sintered using dual alloy method

Exchange interaction and demagnetization process of high-abundance rare-earth magnets sintered using dual alloy method

Hybrid Effect of Exchange Coupling in Ce–Pr–Nd–Fe–B SPSed Magnets by Adding Pr–Fe–B Alloys

In order to obtain high magnetic properties in Ce-Pr-Nd-Fe-B spark plasma sintered (SPSed) magnets, the alloys were introduced by the dual-alloy method. The relationship of microstructure, magnetic properties, and thermal stability was investigated. The remanent magnetization, coercivity, and maximum energy product were sharply enhanced from 0.68 T, 653 kA/m, and 75.62 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> to 0.80 T, 865 kA/m, and 104 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> for the magnets that with 0 and 75 wt.% Pr-Fe-B addition. The Curie temperature also increased from 542 K to 563 K after adding Pr-Fe-B alloys. The scanning electron microscopy (SEM) analysis showed that, during the sintering process, the rare-earth elements migrated into the flake boundary and diffused in 2:14:1 main phases; thus, (Ce, Pr, Nd)2Fe14B hard magnetic phases were formed, which is helpful to optimize the microstructure and magnetic properties. An enhancement of exchange coupling among the grains of SPSed magnets was obtained as a result of grain refinement by adding Pr-Fe-B alloys.

Microstructural design in LaCe misch-metal substituted 2:14:1-type sintered magnets by dual-alloy method

LaCe-based sintered magnets with different microstructural features and distinct rare earth elemental distribution were designed by dual-alloy method. The sample prepared by fine LaCe-containing powder and coarse LaCe-free powder possesses higher remanence (∼13.41 kGs), whereas another sample prepared by fine LaCe-free powder and coarse LaCe-containing powder possesses higher coercivity (∼5.67 kOe). Additionally, these samples are with the same nominal compositions and their elemental distribution features are obviously different in matrix grains respectively. Their remanence difference is mainly affected by the saturation magnetization difference caused by the distribution variation of the rare earth elements at the matrix phase. The coercivity difference is affected by the component of the grain boundary phase between the adjacent grains and the distribution variation of the rare earth elements at the matrix phase. These findings may provide a new prospect for the utilization of LaCe misch-metal in 2:14:1-type permanent magnets.

Magnetic properties, microstructure and magnetization reversal in sintered Nd12.2Fe81.8B6 magnets with the addition of Tb17Fe75B8

Abstract Nd12.2Fe81.8B6 and Tb17Fe75B8 powders were mixed to prepare sintered magnets by the powders preparation, pressing and sintering. With a small addition of Tb17Fe75B8 powders the coercivity increases largely in the Nd-Fe-B/Tb-Fe-B magnets. For the addition of 0.5 g Tb17Fe75B8 (the mass ratio 0.5:9.5 of Tb17Fe75B8 and Nd12.2Fe81.8B6), the coercivity increases to 15.8 kOe, 2.2 times of that in Nd12.2Fe81.8B6. With more amount addition of Tb17Fe75B8 powders the coercivity keeps to increase, and the increase is larger than that of the conventional dual-alloy method. The magnets consist of two main phases, but the atomic interdiffusion is evident for Nd and Tb. Via the investigation of thermal activation it shows that the domain walls size decreases for a little amount addition of Tb17Fe75B8 powders. So the magnetocrystalline anisotropy increases near grain boundary of Nd-Fe-B phase owing to Tb diffusing and substituting for Nd, which is beneficial to the enhancement of coercivity. For the addition of Tb17Fe75B8 more than 0.7 g the domain wall size doesn’t decrease evidently, suggesting that the existing of interfacial exchange coupling which also contributes to the increase of coercivity in the sintered composite magnets.

Microstructure and magnetic properties of multi-main-phase Ce-Fe-B spark plasma sintered magnets by dual alloy method

Abstract Ce-Fe-B spark plasma sintered (SPSed) magnets prepared with different ratio of alloys of Ce-Fe-B and Pr-Nd-Fe-B by dual alloy method are investigated in this paper. As expected, the remanent magnetization Jr, coercivity Hci and maximum energy product (BH)max of SPSed magnets increase obviously with increasing weight percentage of Pr-Nd-Fe-B alloy. The magnetic properties of Jr = 0.71 T, Hci = 915 kA/m, (BH)max = 72 kJ/m3 are obtained for the SPSed magnets with 80 wt% Pr-Nd-Fe-B alloy. There are three Curie temperatures in this type magnet, which implies the coexistence of three hard magnetic phases. The second Curie temperature depends on the Pr-Nd-Fe-B content. With increasing Pr-Nd-Fe-B alloy content, the volume fraction and width of coarse grain zone decrease. It is shown by the microstructure analysis that the rare earth elements diffuse during sintering process resulting in the formation of Pr-Nd-Ce-Fe-B hard magnetic phase. The intergranular exchange coupling strength is enhanced with increasing Pr-Nd-Fe-B content. The present research may be a potential reference for further research and development of this type Ce-containing nanocrystalline permanent magnetic materials.

Significant improvement of the 2:14:1 phase formability and magnetic properties of multi-phases RE-Fe-B magnets with La substitution for Ce

Abstract In this paper, the Ce-Fe-B and (La, Ce)-Fe-B strips were prepared by strip-casting technique and the multi-phases RE-Fe-B (RE = La, Ce, Pr and Nd) magnets were fabricated by dual-alloy method with (Pr, Nd)-Fe-B alloy. The effects of La substitution for Ce on the microstructure of Ce-Fe-B strip-casting alloy were investigated, especially for the formability of 2:14:1 phase. The results showed that the proportion of RE2Fe14B phase significantly increased from 0.0% to 48.0% and the CeFe2 phase drastically decreased from 67.1% to 38.1% with La substitution for 35 wt% Ce in Ce-Fe-B strip-casting alloy. It could be attributed to the enlarged temperature gap between the formation of 2:14:1 phase and Ce2Fe17 phase, which was beneficial for the formability of 2:14:1 phase. Owing to the rise of the proportion of the 2:14:1 phase, the remanence (Br) and maximum energy product ((BH)max) of dual-alloy magnets increased from 11.49 kGs, 28.68 MGOe to 12.38 kGs, 34.76 MGOe with respect to 32.0 wt% Ce or La-Ce substitution content for Pr-Nd, respectively. Meanwhile, the coercivity (Hcj) slightly decreased from 6.49 kOe to 6.16 kOe, which was caused by the decrease of HA (54.09 kOe → 42.37 kOe) and the deterioration of microstructure of the magnet. This work indicated that the cost-effective La-contained RE-Fe-B permanent magnets could be prepared by dual-alloy method.

Magnetic properties of misch-metal partially substituted Nd–Fe–B magnets sintered by dual alloy method**Project supported by the National Natural Science Foundation of China (Grant No. 51590880), the National Key Research and Development Program of China (Grant Nos. 2014CB643702 and 2016YFB0700903), Key Research Program of the Chinese Academy of Sciences of China, and the Inner Mongolia Science and Technology Major Project of

The misch-metal (MM) partially substituted Nd–Fe–B sintered magnets were fabricated by the dual alloy method, and the crystal structure, microstructure, and magnetic properties were analyzed comprehensively. X-ray diffraction (XRD) reveals that the increasing content of the MM has an inconsiderable effect on the crystallographic alignment of the magnets. Grains of the two main phases are uniformly distributed, and slightly deteriorate on the grain boundary. Due to the diffusion between the adjacent grains, the MM substituted Nd–Fe–B magnets contain three types of components with different Ce/La concentrations. Moreover, the first-order reversal curve (FORC) diagram is introduced to analyze the magnetization reversal process, coercivity mechanism, and distribution of reversal field in magnetic samples. The analysis indicates that there are two major reversal components, corresponding to the two different main phases. The domain nucleation and growth are determined to be the leading mechanism in controlling the magnetization reversal processes of the magnets sintered by the dual alloy method.

High performance (La, Ce, Pr, Nd)-Fe-B die-upset magnets based on misch-metal

High performance (La, Ce, Pr, Nd)-Fe-B anisotropic nanocrystalline magnets were fabricated through die-upsetting process by incorporating misch-metal in Nd-Fe-B magnets via dual alloy method. Although coercivity decrease with the increase of misch-metal monotonously, there are no significant decrease in remanence. Magnet with remanence of 13.46 kGs and maximum energy product of 43.5 MGOe was obtained with 30 wt% misch-metal substitution, which is quite promising in practical application. High remanence was resulted from good texture and microstructure analysis revealed that Ce tended to diffuse into 2:14:1 phase uniformly, while the excessive La tended to assemble into the interface of melt-spun ribbons.

Achievement of high performance of sintered R–Fe–B magnets based on misch metal doped with PrNd nanoparticles

The magnetic properties and microstructure of sintered R–Fe–B (R, rare earth) magnets with nominal composition of ((PrNd)1−x MM x )30FebalB1 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.7; MM, misch metal) prepared using dual-alloy method were investigated. For x = 0.3, the maximum energy product ((BH)max) of the sintered magnet is higher than 318.4 kJ·m−3, but intrinsic coercivity (H cj) is lower than 351.8 kA·m−1. The La and Ce contents are obviously different in some matrix-phase grains, which proves that the multi-hard magnetic phases (La, Ce-rich and La, Ce-lean) exist in the magnets. The coercivity is improved by the method of doping PrNd nanoparticles without sacrificing other magnetic properties. An enhancement in coercivity from 517.2 to 872.9 kA·m−1 is achieved by doping 5 wt% PrNd nanoparticles. Meanwhile, it could exhibit better magnetic properties (remanence B r = 1.332 T, intrinsic coercivity H cj = 872.9 kA·m−1, maximum energy product (BH)max = 318.6 kJ·m−3) and make the distribution of the intergranular phase become more homogeneous.

Influence of misch metal content on microstructure and magnetic properties of R–Fe–B magnets sintered by dual alloy method**Project supported by the National Key Research and Development Program of China (Grant Nos. 2014CB643702 and 2016YFB0700903), the National Natural Science Foundation of China (Grant No. 51590880), and the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KJZD-EW-M05).

MM magnets were fabricated by dual alloy method (MM, misch metal). Some magnets have two Curie temperatures. Curie temperatures corresponds to the main phase which contains more LaCe, and decreases from 276.5 °C to 256.6 °C with the content of MM increasing from 30.3 at.% to 50.6 at.%. The variation of with the increase of MM indicates the existence of inter-grain exchange coupling in the magnets. When MM/ at.%, the magnetic properties can reach the level of the intrinsic coercivity kOe and the maximum energy product MGOe. Compared with Nd, La and Ce are easier to diffuse to the grain boundaries in the sintering process, and this will cause the decrease of . Due to the diffusion between the grains, the atomic ratio of La, Ce, Pr, and Nd in each grain is different and the percentage of Nd in all grains is higher than that in misch metal.

Tuning Ce distribution for high performanced Nd-Ce-Fe-B sintered magnets

A dual-alloy method was applied to tune the distribution of Ce for enhancing the performance of Nd-Ce-Fe-B sintered magnets with a nominal composition of (Nd0.75Ce0.25)30.5FebalAl0.1Cu0.1B. In comparison to the single alloy of (Nd0.75Ce0.25)30.5FebalAl0.1Cu0.1B, the coercivity was enhanced from 10.3kOe to 12.1kOe and the remanence was increased from 13.1kG to 13.3kG for the magnets with a dual-alloy method. In addition, the remanence temperature coefficient α and coercivity temperature coefficient β were also slightly improved for the magnet with the dual alloys. The results of microstructure characterizations show the uniform distribution of Ce for the magnet with a single alloy, and the coexistence of the Ce-rich and Ce-lean regions for the magnet with the dual alloys. In combinations with the nucleation of reversal domains and magnetic recoil curves, the property enhancement of magnets with a dual-alloy method was well explained.

Abnormal variation of magnetic properties with Ce content in (PrNdCe)2Fe14B sintered magnets prepared by dual alloy method**Project supported by the National Natural Science Foundation of China (Grant Nos. 51461033, 51571126, 51541105, and 11547032), the Natural Science Foundation of Inner Mongolia, China (Grant No. 2013MS0110), and the Inner Mongolia University of Science and Technology Innovation Fund, China.

Resource-saving (PrNdCe)2Fe14B sintered magnets with nominal composition (PrNd)15−xCexFe77B8 (x = 0−10) were prepared using a dual alloy method by mixing (PrNd)5Ce10Fe77B8 with (PrNd)15Fe77B8 powders. For Ce atomic percent of 1% and 2%, coercivity decreases dramatically. With further increase of Ce atomic percent, the coercivity increases, peaks at 6.38 kOe in (PrNd)11Ce4Fe77B8, and then declines gradually. The abnormal dependence of coercivity is likely related to the inhomogeneity of rare earth chemical composition in the intergranular phase, where PrNd concentration is strongly dependent on the additive amount of (PrNd)5Ce10Fe77B8 powders. In addition, for Ce atomic percent of 8%, 7%, and 6% the coercivity is higher than that of magnets prepared by the conventional method, which shows the advantage of the dual alloy method in preparing high abundant rare earth magnets.

Achievement of high coercivity in sintered R-Fe-B magnets based on misch-metal by dual alloy method

The R-Fe-B (R, rare earth) sintered magnets prepared with different ratio of alloys of MM-Fe-B (MM, misch-metal) and Nd-Fe-B by dual alloy method were investigated. As expected, the high ratio of MM-Fe-B alloy degrades the hard magnetic properties heavily with intrinsic coercivity lower than 5 kOe. When the atomic ratio MM/R ≤ 21.5% the magnetic properties can reach a practical level of Br ≥ 12.1 kGs, Hcj ≥ 10.7 kOe, and (BH)max ≥ 34.0 MGOe. And the effect of Hcj enhancement by the grain boundary diffusion process is obvious when MM/R ≤ 21.5%. It is revealed that the decrement of intrinsic magnetic properties of R2Fe14B matrix phase is not the main reason of the degradation of the magnets with high MM ratio. The change of deteriorated microstructure together with phase component plays fundamental roles in low Hcj. In high MM ratio magnets, (a) after annealing, Ce atoms inside main phase are inclined to be segregated in the outer layer of the main phase grains; (b) there is no thin layer of Ce-rich phase as an analogue of Nd-rich phase to separate main phase grains; (c) excessive Ce tends to form CeFe2 grains.